Apparatus for making oriented webs

ABSTRACT

APPARATUS FOR MAKING AN UNBROKEN POLYMERIC WEB OR FILM HAVING PROJECTING UNORIENTED SECTIONS SURROUNDS BY A PREDETERMINED PATTERN OF UNIAXIALLY AND BIAXIALLY ORIENTED REGIONS.

May 23, 1972 T. H. FAIRBANKS ET AL 3,654,780

APPARATUS FOR MAKING ORIENTED WEBS Original Filed Dec. 17, 1970 a n n a n n an n p Ann m 2 A United States Patent Office 3,664,780 Patented May 23, 1972 3,664,780 APPARATUS FOR MAKING ORIENTED WEBS Theodore H. Fairbanks, Liverpool, Robert F. Gillespie, Havertown, and Dorsey C. Nelson, Springfield, Pa., assignors to FMC Corporation, Philadelphia, Pa. Original application Dec. 17, 1968, Ser. No. 784,382, now Patent No. 3,574,809. Divided and this application Aug. 5, 1970, Ser. No. 61,187

Int. Cl. 329d 7/00 U.S. Cl. 425-66 4 Claims ABSTRACT OF THE DISCLOSURE Apparatus for making an unbroken polymeric web or film having projecting unoriented sections surrounded by a predetermined pattern of uniaxially and biaxially oriented regions.

This application is a division of our application Ser. No. 784,382, filed Dec. 17, 1968, now U. S. Pat. 3,574,809.

The present invention is directed to an improved apparatus for making polymeric webs or films which possess high strength, stiffness and tear resistant properties.

U.S. Pat. 3,386,876, issued on June 4, 1968, to H. W. Wyckoff, discloses a method and apparatus for making a nonwoven net structure by providing an unoriented film of thermoplastic polymeric material with a predetermined pattern of openings so as to shape the film areas between such openings into the form of ribs, each having a narrow part and being of greatest width at its ends, and thereafter stretching such perforated film at least along one of its biaxial directions to enlarge the openings and uniaxially draw at lea-st certain of such ribs. While some latitude is permitted in the shaping and spacing of the openings initially formed in the film and the forces applied during stretching, these factors are regulated to restrict orientation to only selected areas of the film, and more specifically to insure that the oriented ribs terminate at or are connected by undrawn film portions or junctures.

During the stretching of the perforated film, the ribs are progressively oriented in the direction of the applied stretching force or forces; that is, with uniaxial drawing in each successive group of parallel ribs occurring simul taneously and extending to a predetermined degree along such ribs before drawing starts in adjacent groups of ribs which are in the series therewith. In accordance with the teachings of this Wyckotf patent, to insure proper stretching two basic requirements must be met, as follows:

(1) ribs which are to draw in parallel with each other must be capable of being drawn to substantially the same amount, and

(2) ribs which are to be drawn in series with each other must be of comparable cross-section so that stretching will be initiated in a group of undrawn ribs after drawing is completed in an adjacent group of ribs and before such drawn ribs are stretched beyond their breaking point or a predetermined point compatible with other drawing which is to be or has been accomplished.

More particularly, the above-noted Wyckoff patent teaches that the openings formed in the unoriented film are spaced so that the ratio between the widest and narrowest parts of the ribs is at least equal to the ratio between the load required to initiate drawing of such ribs and the load necessary for maintaining such drawing once the ribs have yielded. When such ribs have been stretched to the maximum allowable degree the line defining the end of a drawn rib, which is referred to in the Wyckofi patent as a draw-line, will have approximately the maximum length possible without having the junction between the ends of adjacent ribs stretch and without having the draw-line of one rib interfere or cross with the draw-lines of the other ribs at such juncture.

In applications where a perforated finished product is unsatisfactory, the above-noted patent teaches that selected spaced areas of an unoriented thermoplastic film may be painted, dyed or otherwise coated with a black or other heat absorbing pigment. These coated areas would correspond to openings formed in the film and, upon biaxially stretching such film under hot drawing conditions, as with radiant heating, the coated areas would absorb the greatest amount of heat and, therefore would yield, Without being oriented, when the film is subjected to stretching forces. On the other hand, only the uncoated rib areas would react to the stretching forces exerted along their respective longitudinal axes and would be uniaxially drawn, while the junctures between the drawn ribs would remain undrawn.

As a still further alternative the Wyckoff patent teaches that in lieu of or in combination with the coating procedure described above, a heat reflective material, such as aluminum paint, may be applied to the unoriented film of polymeric material in accordance with a predetermined pattern corresponding to the desired arrangement of ribs and undrawn junctures. Upon biaxially orienting of such film under hot drawing conditions, the rib areas coated with the heat reflective material would be heated the lea-st and would undergo uniaxial orientation, while the coated areas would yield along biaxial directions.

During the stretching of a film coated with a heat absorbing and/ or heat reflecting material in accordance with the Wycko'ff patent teachings, the coated areas of the film would yield and thus the coatings thereon would gradually become thinner and progressively less efiicient in performing their intended functions with the continued stretching of the film.

U.S. Pat. 3,255,065, issued on June 7, 1966, to H. W. Wyckoff, discloses a method and apparatus for making a composite film by laminating or otherwise uniting an unbroken and unoriented film of thermoplastic polymeric material with a similar film having a predetermined pattern of openings, as disclosed in the Wyckolf Pat. 3,386,- 876, and thereafter stretching of the laminated structure along desired directions.

Upon stretching of such laminated structure along its longitudinal and transverse axes, the portions of the unbroken film which extend across the openings in the perforated film are biaxially oriented. The ribs of the perforated film, and the portions of the unbroken film attached thereto, are uniaxially oriented and impart desired stiffness into the resulting composite film, while the areas of the laminated structure which are located between the ends of such ribs remain undrawn.

The manufacture of composite films by the method described in the Wyckotf Pat. 3,255,065 requires the production of Separate unoriented films of thermoplastic polymeric material, the perforating of one of such films, the laminating of the unperforated and perforated films, and finally the biaxial stretching of the laminated structure. These numerous manipulative steps, taken with the critical care which must be exercised to insure proper film perforation and lamination render this patented method slow and costly.

A primary object of this invention is to provide a new or generally improved and more satisfactory apparatus for making a polymeric web or film having good strength and stiffness along desired directions and which exhibits improved tear resistant characteristics.

Another object is the provision of an improved apparatus for providing a web or film of polymeric material having projecting unoriented sections surrounded by a predetermined pattern of uniaxially and biaxially oriented regions.

Still another object of this invention is an apparatus which facilitates a controlled orientation of an unperforated web or film along selected areas thereof.

A further object is the provision of an apparatus for making an unbroken polymeric web having a network of uniaxially oriented regions extending longitudinally and transversely of the web and which are separated at their ends by projecting unoriented sections.

For a greater understanding of this invention, reference is made to the following detailed description and drawing in which FIG. 1 is a diagrammatic side view of the apparatus of the present invention;

FIG. 2 is a fragmentary front view of a portion of an extrusion die employed in the apparatus shown in FIG. 1;

'FIG. 3 is a perspective view of a portion of a web of polymeric material formed by a portion of the apparatus of the present invention;

FIG. 4 is a perspective view of the web shown in FIG. 3 after longitudinal stretching of the same by another portion of the apparatus of the present invention;

FIG. 5 is a plan View of the web shown in FIG. 3 after being subjected to biaxial stretching forces; and

FIGS. 6 and 7 are views similar to that of FIG. 2 illustrating portions of further embodiments of extrusion dies which are adapted for use in the apparatus shown in FIG. 1.

The above and other objects of the invention are achieved by an apparatus in which a polymeric filmforming material is initially shaped into an unoriented web having continuous, alternate thick and thin portions extending longitudinally thereof, with each of the respective thick and thin portions of the web being of substantially uniform cross-section throughout its length. Areas extending transversely of such web, at longitudinally spaced intervals thereof, are then stretched in a longitudinal direction whereby sections of the thick and thin portions of the web within the stretched areas are reduced in thickness and the molecules thereof are oriented in the longitudinal direction of the web. The web is then stretched in its transverse direction to reduce the thick ness of all of the web portions defined by the original continuous thin portions of the web and to orient the molecules thereof in the transverse direction of the web. In the resulting stretched web the remaining sections of the original thick portions are unoriented. Regions of the stretched web extending between such remaining original thick sections of the web in both the longitudinal and transverse direction are uniaxially oriented in their respective directions, while all other regions of the web are 'biaxially oriented.

In the shaping of the unoriented web, the continuous thick portions thereof may project from one or both sides of the web. In the latter instance, it is necessary that the thick portions projecting from one side of the web be aligned with the thick portions projecting from the opposite side of such web. The widths of the respective thick and thin portions of the web are equal and in the preferred construction the widths of all of the thick and thin portions are substantially the same.

The widths and spacing of the transverse areas of the unoriented web which are stretched in a longitudinal direction may be varied. Preferably, however, the widths of such areas and their longitudinal spacing is substantially equal to the widths of an individual thick portion of the original web.

The degree to which the web is stretched in its longitudinal and transverse direction only may also differ. In the preferred embodiment, the web is stretched equally in both its longitudinal and transverse directions. The degree of stretching is such as to provide the resulting oriented web with the most desirable strength, stiffness and tear resistant properties. Desirably, the degree of biaxial stretching is such that the lines defining the ends of the uniaxially drawn regions terminate at undrawn web portions without intersecting with each other. The thick portions of the web are such that, under the stretching conditions noted above, the stretched sections of such thick web portions are reduced to a thickness substantially equal to the thickness of the original thin web portions.

Oriented webs made with the apparatus of the present invention are adapted for a variety of uses, for example, as protective coverings or shields, as in building construction, as wrapping and bagging materials, as inflatable structures, such as observation balloons, life rafts, etc.

The apparatus of the present invention is adapted for use with thermoplastic polymeric materials, such as polypropylene, polyethylene, polyesters, etc., as well as orientable polymeric film-forming materials which are converted into integral webs by chemical reactions, such latter material including, for example, viscose.

More particularly, the apparatus of the present invention includes means for shaping fiowable polymeric filmforming material into a continuous stream having continuous, alternate thick and thin portions extending longitudinally thereof with each of the respective thick and thin portions of such stream being of substantially uniform cross-section throughout its length, means for setting the shaped stream of film-forming material to provide an unoriented, self-supporting web, means for stretching the Web in its longitudinal direction at longitudinally spaced intervals thereof, and means for stretching the longitudinally stretched web in its transverse direction. Intermittent longitudinal stretching of the web as mentioned above may be achieved by advancing the web between spaced pairs of positively driven nip rolls, with the leadmg pair of such nip rolls being rotated at a more rapid rate than the trailing pair of such nip rolls and with at least one roll of the trailing pair of nip rolls formed with continuous grooves extending longitudinally thereof at spaced intervals along its peripheral surface so that the web is periodically gripped thereby during its advancement.

For a more detailed description of the apparatus of the present invention, reference is made to FIG. 1 of the drawing wherein character 15 designates a nozzle or die from which is extruded a shaped unbroken stream 17 of molten thermoplastic polymeric film-forming material, such as polypropylene. The extruded stream 17 is set in any convenient manner to provide a self-supporting web 19. Quenching of the extruded stream of molten thermoplastic material may be effected by a bath of cool water 21 contained within a tank 23. An immersion roll 25 is located well within the tank 23 for reversing the travel of the web 19 and directing the same to a guide roll 27.

Illustrated in FIG. 2 are die lips or blades 29 and 31 of the nozzle 15 which together define an elongated orifice 33 of desired configuration. The surface 35 of the die lip 29 is substantially fiat while the opposing surface 37 of the die lip 31 includes a series of spaced grooves 39 which extend substantially perpendicular to the length of such lip. The stream 17 of molten thermoplastic material assumes the shape imparted thereto by the opposing surfaces of the die lips 29 and 31 and, when quenched, provides a resulting web 19 with continuous, alternate thick and thin portions 41 and 43, respectively, which extend the length thereof, as shown in FIG. 3. Each of the respective thick and thin portions 41 and 43 of the web 19 is of substantially uniform cross-section throughout its length and, in the particular Web illustrated, the thick and thin web portions are substantially of uniform width. The difference in thickness between the thick and thinner portions of the web may be varied as more fully discussed hereafter.

In lieu of the web construction described, a web having thick portions or ribs 41 projecting from the opposite sides thereof is equally satisfactory for use in the method which has been disclosed, providing that such thick portions or ribs 41 along one side of the web are aligned or alternated with the thick portions along the opposite sides thereof. As hereafter described, such modified web may be formed simply by initially shaping a molten thermoplastic material between die lips having opposing surfaces which correspond to the surface 37 of the die lip 31.

Referring again to FIG. 1 of the drawing, a formed web 19 is continuously advanced out of the quenching bath and over the guide roll 27 by a pair of pull rollers 45 which are driven by suitable means, not shown, in the directions as indicated by arrows. Beyond the pull rollers 45 the web .19 travels between pairs of nip rolls 47 and 49, which are positively driven in the directions as indicated by arrows, and then into a conventional tenter frame designated generally by the character 51. During travel between the pairs of nip rolls 47 and 49, areas extending transversely of the web 19 at longitudinally spaced intervals thereof are stretched in the longitudinal direction as indicated at 53 in FIG. 4.

This desired stretching is achieved by intermittently gripping, the web 19 by the pair of nip rolls 47, while the pair of nip rolls 49 are driven at a constant but faster rate of speed than the pair of nip rolls 47. This procedure is preferably achieved by an apparatus as illustrated in FIG. 1 in which at least one of the nip rolls 47 is formed with like, continuous longitudinal grooves 55 which are spaced at uniform intervals along the roll periphery, while the remaining nip rolls are of conventional construction, with each having a smooth, continuous annular peripheral surface 57.

Sections of both the thick and thin portions 41 and 43 of the web 19 within the stretched areas 53 are, of course, reduced in thickness and the molecules thereof are oriented in the longitudinal direction of the web. As heretofore mentioned, the degree to which the areas 53 are longitudinally stretched may be varied, but is preferably such as to reduce the original thickness of the thick portions 41 of the web in such areas 53 to generally the original thickness of the thin Web portions 43. The longitudinally stretched web leaving the nip rolls 49 and passing into the'tenter frame 51 has an appearance as shown in FIG. 4, in which each of the original continuous thick portions 41 have been reduced to a series of longitudinally spaced sections or projections 59.

In the tenter frame 51, the longitudinal edges of the web 19 are gripped at closely spaced intervals and directed along diverging paths concomitantly with longitudinal advancement of the web to thereby stretch the web in its transverse direction. This transverse stretching of the web is preferably to substantially the same degree as the longitudinal stretching to which such web had been previously subjected. Transverse stretching is confined substantially to the original continuous thin. portions 43 of the web 19; that is, the continuousportions of the web which extend between adjacent rows of the longitudinally aligned portions of the thick sections or projections 59 shown in FIG. 4.

In the resulting web leaving the tenter frame 51, as illustrated in FIG. 5, the remaining sections of the original web thick portions 41 remain unoriented. Regions 61 and -63 which extend, respectively, longitudinally and transversely between adjacent of such unoriented thick portions or projections 59 are uniaxially oriented in their respective directions, while all other regions of the web, as indicated at 65, are biaxially oriented.

The uniaxially oriented regions 61 and 63 impart stiffness into the web 19 in their respective directions of orientation and, together with the biaxially oriented regions 65, improve the web tensile strength properties. The unoriented areas 5-9 are well isolated from each other between the surrounding oriented regions 61 and 63 and serve to arrest tearing which may have initiated the other areas of the web.

As heretofore mentioned, the web 19 may be provided with thick portions or ribs 41 projecting from opposite sides thereof. Such webs may be formed by an extrusion die as shown in FIG. 6 wherein spaced die lips 67 and 69 are each provided with a series of spaced grooves 71 along opposing surfaces thereof with the grooves 71 in the die lip 67 being aligned with the grooves 7-1 in the die lip 69. Alternatively, an extrusion die as shown in FIG. 7 may be employed, wherein spaced die lips 73 and 75 are each provided with a series of spaced grooves 77, but with the grooves 77 in the die lip 73 being in staggered relationship with the grooves 77 in the die lip 75.

Webs 19 produced with the modified extrusion dies described above will include continuous, alternate thick and thin portions 41 and 43, respectively. With the extrusion die shown in FIG. 6, aligned thick portions 41 will, of course, project from opposite sides of the resulting web 19. The extrusion die shown in FIG. 7 will also provide for a web 19 having thick portions 41 project ing from its opposite sides. In this instance, however, the thick portions 41 along one side of such web 19' will be staggered relative to the thick portions 41 along the opposite side of such web.

We claim:

1. Apparatus for making a polymeric web having a predetermined pattern of unoriented and molecularly oriented portions including means for forming a solidified 'unoriented web of polymeric material having continuous,

alternate thick and thin portions extending longitudinally thereof with the respective thick and thin portions of such web being of like and substantially uniform cross-section throughout their lengths, and means for stretching the formed web along biaxial directions, said stretching means including a first pair of nip rolls having continuous peripheral surfaces for engaging opposite sides of the web, means for positively driving said nip rolls at a uniform rate of speed for continuously advancing the Web in a longitudi nal direction, a second pair of nip rolls positioned in trailing relationship with and spaced from said first pair of nip rolls for engaging with opposite sides of the web, said first and second pairs of nip rolls being of such length as to extend tranversely across the entire width of the web which is being stretched, at least one of the rolls of said second pair of nip rolls having an interrupted peripheral surface formed by continuous grooves extending longitudinally thereof at arcuately spaced intervals along its peripheral surface, and means for positively driving said second pair of nip rolls at a uniform rate of speed which is less than that of said first pair of nip rolls.

2. Apparatus as defined in claim 1 wherein said web forming means includes a pair of die blades disposed in spaced apart relationship whereby opposing surfaces thereof together define a die orifice having an entrance and exit end, means for delivering a flowable, film-forming polymeric material under pressure to the entrance end of said die orifice, like, spaced grooves formed in at least one of the opposing surfaces of said die blades and extending between the entrance and exit ends of said die orifice whereby the fiowable film-forming material is shaped 7 into a continuous stream having continuous, alternate thick and thin portions extending longitudinally thereof as it passes through and issues from said die orifice, and means for setting the shaped stream of film-forming material to provide a web.

3. Apparatus as defined in claim 2 wherein spaced grooves are formed in both of the opposing surfaces of said die blades, with the grooves in one of said opposing surfaces being aligned with the grooves in the other of said opposing surfaces.

4. Apparatus as defined in claim 2 wherein spaced grooves are formed in both of the opposing surfaces of said die blades with the grooves in one of said opposing surfaces being staggered relative to the grooves in the other of said opposing surfaces.

References Cited UNITED STATES PATENTS Milne 181 FB X lVeit.

Schuetz et al. 1810 Trainer 181 PB X McCreary.

Laurie.

LeMoine et a1. 18--1 FB H. A. KILBY, JR., Primary Examiner US. Cl. X.R.

15 18-10, 19 RR, Dig. 53; 42571, 396

*zgyggy UNITED STATES [PATENT OFFICE I CERTIFICATE OF CORRECTION Patent No. 3 Dated may 23 1972 Inventor s Theodore H. Fairbanks; Robert F. Gillespie and Dorsey C. Nelson It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4, line 45, after "direction" and before "at" insert --only-. Col. 5, line 38, delete the comma after "gripping".

Signed and sealed this 12th day of September 1972.

(SEAL) Attest:

FDWAPP M .FLETCHEP ,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

